It is known that the physicochemical properties of solids in particulate form are influenced by the size and shape of the particles. As particle size of solids diminishes in scale, there is an enhancement of properties, and often the inception of new properties. Investigators are finding that nanostructural materials can exhibit unique mechanical, electronic and optical properties.
New commercial products are becoming available which provide special advantage because of fine particle size. Zinc oxide is widely utilized as an ingredient in human health products. Superior results are now obtained by the use of submicron transparent zinc oxide powder. The ultrafine zinc oxide provides advantage for UVA/B-protection in cosmetic formulations, and exhibits enhanced antimicrobial capacity and functions as a preservative.
Alkali metal bicarbonate is another commodity reagent which has found application in a broad variety of products such as laundry detergents, deodorizers, creams and lotions, dentifrices, antacids, buffers, fungicides, and the like.
There is evidence that fine particle size alkali metal bicarbonate or ammonium bicarbonate can exhibit increased reactivity in comparison with coarse grain bicarbonate salts. In soda cracker production, finely divided sodium bicarbonate ingredient is more efficiently distributed and effectively reactive during the cracker dough preparation. The finished baked cracker is an improved product which has a substantially uniform texture, flavor and surface color, and a consistent pH throughout.
The inclusion of particulate alkali metal bicarbonate in an antiperspirant-deodorant cosmetic stick provides a product with improved deodorant properties. However, coarse grains alkali metal bicarbonate has an undesirable tendency to settle in an antiperspirant-deodorant cosmetic stick matrix. The use of ultrafine alkali metal bicarbonate as a deodorant ingredient in cosmetic stick and roll-on type personal care products is being investigated, since the ultrafine particles have less tendency to settle than coarse grain particles when dispersed in a liquid or semi-solid matrix.
A limiting factor has been the unavailability of alkali metal bicarbonate or ammonium bicarbonate powder which is composed of free-flowing ultrafine particles that are not in an agglomerated state.
There is continuing interest in the development of reagents such as alkali metal bicarbonate and ammonium bicarbonate which have an ultrafine particle size, and exhibit a novel combination of properties when utilized as an ingredient in personal care, biologically active, household, and specialty type products.
Accordingly, it is an object of this invention to provide particulate alkali metal bicarbonate and ammonium bicarbonate having an ultrafine particle size, and a surface area of at least about ten square meters per gram.
It is another object of this invention to provide alkali metal and ammonium bicarbonate powder having a submicron particle size, and which is free-flowing and essentially free of agglomerated particles.
It is a further object of this invention to provide a process for producing an ultrafine bicarbonate salt composition which is a co-micronized blend of crystalline compounds having a submicron particle size range.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.
Publications of background interest with respect to the present invention subject matter include U.S. Pat. Nos. 2,378,147; 3,241,977; 4,997,454; and 5,147,631.